Diversity of the bacterial communities in Anthropogenic Black Earth from the Central and Oriental Amazon

Keywords in English

16S rRNA
Bacterial Diversity
Black Earth
Diversity Index.
Sequencing

Abstract in English

Anthropogenic Dark Earth (ADE) is one of the most fertile soils in the world. ADE soils have received this nomination due to the pre-historical origin of these archaeological sites, established by pre-colombian populations. ADEs are small areas of soil which present high nutrient and organic matter contents and are randomly distributed throughout the Amazonian region. The true origin of these soils is not known yet. Due to the lack of information concerning the bacterial diversity, this work studied the bacterial diversity in ADE soils collected from two regions: Lagoa Balbina - site Terra Preta (Central Amazonia- Amazonas state) and National Forest of Caxiuanã - archaeological site Mina I (Oriental Amazonia - Pará state), using culture-independent molecular techniques. The total genomic DNAs extracted from the soil samples were used as templates in the PCR reactions using the universal primers for the 16S rRNA bacterial gene. The PCR-products were cloned into the pGEM-T vector and 980 clones were selected and searched using the GenBank (NCBI-USA) and the RDP II program. Data analyses indicated predominance of unknown microorganisms, representing 41.6 % among the sequences from ADE-Balbina, 68.3 % from Adjacent-Balbina, 84.8% from ADE-Mina and 47.7 % from Adjacent-Mina. The predominant phylum in ADEBalbina was Firmicutes, representing 37.1% of the total sequences from that site, followed by Proteobacteria (9.6%), Verrucomicrobia (5.6%) Acidobacteria (2,5%), Gemmatimonadetes (2,5%), Actinobacteria (0,5%) and Nitrospira (0.5%). On the other hand, in the adjacent soil ADJ-Balbina, the predominant phylla were Proteobacteria (15.1%), Acidobacteria (12.5%), Firmicutes (2.3%), Nitrospira (1.1%) and Verrucomicrobia (0.8%). In the Oriental Amazon, the prevalent phylla from the ADE-Mina soil were Proteobacteria (6.5%), Acidobacteria (4.7%), Firmicutes (1.4%), Nitrospira (1.1%), Planctomycetes (1.1%) and Verrucomicrobia (0.4%). In the ADJ-Mina verificou a presença dos filos Acidobacteria 27.2%, Proteobacteria 14.2%, Firmicutes 3.8%, Verrucomicrobia 3.8%, Nitrospira 1.3%, Planctomycetes 1.3%, Actinobacteria 0.4% e Gemmatimonadetes 0.4%. The soil pH may be of the soil attributes which may have directly influenced the bacterial diversity in those soils, as well as the above-ground vegetation from the natural forest in Caxiuanã-Pará. The estimates of the Operational Taxonomic Units (OTUs) richness using Bootstrap directly corroborated the diversity values obtained from the Simpson and Shannon indexes. Unique UTOs using Jackknife estimator were correlated with a higher percentage of the low frequencies of phylla in all the four clone libraries. The nonparametric ACE and Chao1 methods to estimate the OTUs richness also corroborated the Jackknife values.

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